Thermo-electric method for texturing of glass surfaces

ABSTRACT

A thermo-electric method for texturing a glass surface including, for example, simultaneously heating a glass substrate to a temperature less than its glass transition temperature and applying a bias across the glass substrate using a template electrode. The applied bias at the processing temperature induces localized ion migration within the glass, which results in the formation in the glass surface of a negative topographical image of the pattern formed in the electrode.

BACKGROUND

The present disclosure relates generally to the texturing of glasssurfaces, and more particularly to a thermo-electric method forselectively inducing ion migration within a glass substrate to form atextured surface on the substrate.

The ability to create topographical features in glass surfaces is ofinterest for a variety of applications. Surface texturing can be used,for example, to modify the optical properties of a glass substrate.Topographical features in glass surfaces can be used to createanti-reflective or anti-glare surfaces, and custom patterns likediffraction gratings can produce optical scattering for light-trapping.Tailored surface topography can also be useful for controllingelectrostatic discharge and for affecting other properties such aswetting behavior, adhesion, and general aesthetics through the creationof surface roughness or discrete surface features.

A number of methods can be used to form textured glass surfaces. Forexample, glass substrates can be coated with a texturized layer. Incontrast to such surface coatings, a variety of “direct-write”techniques that incorporate robust, chemically durable, and stronglyintegrated patterning directly into the surface of the glass itself areof significant interest. However, most direct-write methods involveeither (i) a mask-and-etch approach to provide selective surfacemodification using corrosive solutions or ion bombardment, or (ii)high-temperature processing, where the glass is embossed by heating toabove its glass transition temperature (T_(g)).

In view of the foregoing, it would be advantageous to provide“direct-write” texture or patterns in a glass surface, without the needfor a separate etch step, and at relatively low processing temperatures,i.e., below the glass transition temperature of the glass.

SUMMARY

A method for forming texture in a surface of a glass substrate includesproviding a glass substrate comprising a glass material having a glasstransition temperature, contacting a surface of the glass substrate witha template electrode, heating the glass surface to a temperature lessthan the glass transition temperature, and applying a DC bias to theelectrode effective to transport ions within the glass substrate andform a textured glass surface. The template electrode can be maintainedin physical contact with the glass surface during acts of heating andapplying, for example, by moving the template electrode with respect tothe glass substrate, by moving the glass substrate with respect to thetemplate electrode, or a combination of both.

In embodiments, glass surface is heated to a temperature at least 150°C. less than the glass transition temperature of the glass substrate.For example, the glass surface can be heated to a temperature in a rangeof 100 to 300° C. or 300 to 600° C. In order to induce the migration ofpositive ions within the glass substrate, a voltage is applied such thatthe template electrode is positively biased with respect to the glasssubstrate.

The method can be applied to glass substrates having a variety of glasscompositions, including glass substrates where a bulk composition of theglass material includes less than 1 mol % alkali metal oxide or alkalineearth metal oxide (e.g., less than 1 mol % alkali metal oxide). Inrelated embodiments, the textured surface can be differentially etchedwith a subsequent HF-etching step to enhance/control the feature size.

A further method for forming texture in a surface of a glass substratecomprises contacting a glass surface of a glass substrate and a templateelectrode at from 20° C. to less than the glass transition temperatureof the substrate, and applying a DC bias to the electrode effective totransport ions within the glass substrate and form a textured glasssurface. The glass substrate may be actively heated or cooled during thecontacting and applying in order to maintain the contacted surface at adesired temperature.

The disclosure further relates to an article having a glass surfaceformed by the method. In such an article, the glass surface comprises aglass material having a bulk composition and a textured region formed ina surface of the glass material. The textured region comprises aplurality of raised and lowered features, the raised features havingsubstantially the same composition as the bulk composition, and thelowered features being deficient with respect to the bulk composition inat least one alkali, alkaline earth or transition metal. For instance, acomposition of the at least one alkali, alkaline earth or transitionmetal in the lowered features can be less than 50% (e.g., less than 50,20 or 10%) of the corresponding bulk composition.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the invention as described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed. Theaccompanying drawings are included to provide a further understanding ofthe invention, and are incorporated into and constitute a part of thisspecification. The drawings illustrate various embodiments of theinvention and together with the description serve to explain theprinciples and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustrating an embodiment of the disclosedthermo-electric glass-texturing process;

FIG. 2A is an optical micrograph of a templated electrode;

FIG. 2B is a higher magnification image showing the templated topographyof the electrode in FIG. 2A;

FIG. 3 is an optical micrograph of a textured surface in a sodiumaluminosilicate glass substrate;

FIG. 4 is an optical micrograph of a textured surface in a bariumboroaluminosilicate glass substrate;

FIG. 5A is an optical profilometer height image of the sodiumaluminosilicate glass substrate of FIG. 3 before texturing;

FIG. 5B is a corresponding profilometer image of the same glasssubstrate after texturing;

FIG. 6A is an optical profilometer height image and the associatedprofilometer trace of a templated electrode;

FIG. 6B is the corresponding height image and trace of a glass substratefollowing texturing with the templated electrode of FIG. 6A;

FIGS. 7A-7C are optical profilometer height images of templatedelectrode according to various embodiments;

FIG. 7D shows histograms of the height distributions in textured glasssubstrates;

FIGS. 8A and 8B are cross-sectional SEM micrographs of a textured glasssubstrate;

FIG. 8C is a backscattered image showing relief topography in a texturedglass substrate;

FIG. 8D is an SEM micrograph of a textured glass substrate followingoptional chemical etching; and

FIG. 9 shows energy-dispersive x-ray spectra for a textured glasssubstrate.

DETAILED DESCRIPTION

A method is disclosed for texturing a surface of a glass substrate. Themethod utilizes a template electrode, which is provided with topographicfeatures to be transferred to the glass. The template electrode isbrought into contact with a surface of the glass to form a templateelectrode-glass substrate assembly and the glass substrate is thenheated to a temperature less than its glass transition temperature whilea DC bias is applied across the substrate. The DC bias is chosen suchthat the template electrode is positively biased relative to the glass.In an embodiment, an AC voltage can be overlaid with a DC bias toachieve the desired effect.

As an electrode, the template electrode comprises anelectrically-conductive material that can be adapted to provideelectrical contact with the glass substrate. An effective templateelectrode is more electrically-conductive than the glass such that itcan provide the desired level of electric field uniformity over thetexturing area. The template electrode may be formed from a metal,semiconductor, semimetal, or conductive non-metal. In embodiments, thetemplate electrode material has a sufficiently high viscosity at theprocess temperature such that the electrode topography is retained overthe desired process timeframe.

As a template, the template electrode includes a surface with atopography intended to be conveyed, in a negative sense, to the glasssurface. The size and dimension of the topography is not limited, andmay include features characterized by a length scale in the range ofnanometers, micrometers or larger.

During the process, the combination of voltage and temperature inducesion migration within the glass proximate the interface with the templateelectrode, the net effect of which is a semi-conformal adapting of theglass surface topography to the template topography, which results inthe formation in the glass surface of a negative topographical image ofthe texture formed in the electrode. After the electrode pattern isincorporated into the glass substrate, the glass can be cooled and theelectrode separated from the glass.

The texturing can be formed over a portion or substantially all of amajor surface of the substrate. The texturing can include a regular orperiodic pattern or shape such as lines, gratings, arrays, channels, orother shapes. Shapes may be arranged concentrically. Further exampletexturing is random, pseudo-random or aperiodic, and can include bumps,divots, hillocks, pillars, matte-finish, as well as light-trapping orlight-scattering texture including roughness over a variety of lengthscales. A surface having texture may be an engineered surface, e.g.,microlens, Fresnel lens, Lotus-leaf, moth-eye, waveguide or otherlight-guiding structure. Individual textured features may have a varietyof cross-sectional shapes, including square, circle, oval, triangle,etc. Shaped features may be convex or concave such as convex or concavespheroids or ovoids.

The magnitude of applied voltage can range from 100V to 10,000V, and candepend, for example, on the composition of the glass substrate and thegeometry of the texture. For instance, in the case of low-resistivity,high-alkali content glasses, voltages in the range of 100V to 1,000V canbe used, while for high-resistivity, alkali-free glasses, highervoltages in the range of 1,000V to 10,000V, e.g., 2000 to 4000V can beused.

The voltage may be applied in a series of steps to achieve a maximumdesired value, or ramped in a current-limited configuration to a processvoltage. The latter approach can be used to obviate thermal dielectricbreakdown caused by the passage of excess current through the glasssubstrate. Alternatively, because breakdown strength of the glass varieswith glass composition, surface texture and chemistry, ambienttemperature, in addition to other factors, an “instant-on” approach forapplying the voltage may be used under some conditions. Thicker glasswould also generally allow for application of higher voltages whileavoiding electrical breakdown.

The voltage can be applied for a period of time in the range of 1 minuteto several hours, e.g., from 5 to 60 minutes or from 15 to 30 minutes.The glass substrate can then be cooled to about room temperature andseparated from the template electrode. The applied voltage may beremoved prior to cooling, or after cooling.

A system for executing the disclosed process may comprise suitable heatand voltage sources that can be adapted to simultaneously heat and biasa template electrode-glass substrate assembly in a controlled manner. Inan embodiment, the system can be used to control the process atmosphere.Texturing under either vacuum, inert gas (e.g., dry N₂), or permeablegas (e.g., He) can help minimize atmosphere effects that might bedetrimental to the process.

The disclosed method can be applied to a variety of different glasscompositions, including alkali-free and alkali-rich glasses, and can becarried out at processing temperatures that are substantially less thanthe glass transition temperature (T_(g)) of the glass substrate.

As used herein, the term “alkali” refers to alkali metals (e.g., Li, Na,K, Rb and Cs) and “alkaline-earth” refers to alkaline-earth metals(e.g., Be, Mg, Ca, Sr and Ba) unless the context clearly indicatesotherwise. In addition to being applicable to alkali-rich glasses, whichcontain a relatively high concentration of mobile alkali ions (e.g.,greater than 1%), the disclosed method may be used with low-alkaliglasses, including alkali-free glasses. Low-alkali glasses of commercialand technical interest often contain a significant concentration ofalkaline-earth metals in their composition to achieve the desiredproperties.

The alkali and/or alkaline earth oxides in a glass matrix, in contrastto glass network formers such as Si, B, and Al, do not participate informing the network structure. Alkali and alkaline earth oxides areinstead considered network modifiers. Network modifiers may increase thecoordination of network former cations like B, help to charge-compensateAl in silicate glasses, or create non-bridging oxygens by breakingSi—O—Si bonds, for example. Example low-alkali glasses have an alkalimetal oxide content of less than 1 mol. % (e.g., less than 0.5, 0.2, 0.1or 0.05 mol % alkali). As network-modifier elements like alkali andalkaline-earth elements are typically more weakly-bound into the networkstructure of the glass, it is these species that will typically exhibitsubstantial mobility under electric fields. In this context, themigration of ions in the glass is often used implicitly to describe themigration of these mobile species with respect to the remainder of theglass network. Ion-depleted regions of the glass surface proximate tothe template electrode thus also describe a glass composition where thenetwork-modifier species—alkali and/or alkaline-earth ions—are depleted,with the network-forming species remaining and comprising the vastmajority of the composition in said layer.

Glasses are usually formed by solidification from the melt. The glassystate can be distinguished from the liquid state through a number ofphysical properties, including atomic structure and manytemperature-dependent physical properties like volume expansion, heatcapacity, etc. The formation of a glass from a liquid can be describedin a plot of specific volume as a function of temperature. On cooling aliquid, there is a discontinuous change in volume at the melting pointif the liquid crystallizes. However, if no crystallization occurs, thevolume of the liquid decreases at about the same rate as above themelting point until there is a decrease in the expansion coefficient ata range of temperature called the glass transformation range. Below thistemperature the glass structure does not relax at the applied coolingrate. If slower cooling rates are used so that the time available forthe structure to relax is increased, the super-cooled liquid persists toa lower temperature, and a higher-density glass results. The glasstransition temperature corresponds to the temperature at which a givenglass composition will exhibit a viscosity of 10¹³ Poise (or 10¹² Pa-s)within the glass transformation range, and is often taken as a usefulprocess parameter for delineating between when a glass is effectivelysolid versus liquid over convenient timescales.

Applicants have surprisingly determined that the disclosedthermo-electric texturing can be performed by heating the glasssubstrate to a temperature that is significantly less than its glasstransition temperature (T_(g)). A temperature that is significantly lessthan the glass transition temperature is at least 150° C. less thanglass transition temperature, e.g., at least 150, 200, 250 or 300° C.less than T_(g). Appreciating that a reduced viscosity and bulkvolumetric relaxation is an inherent part of the mechanism by which thetopography forms in texturing glass by other methods like hot-embossing,one would assume that a necessary processing temperature would be at oreven greater than the glass transition temperature. Lower processtemperatures are desirable, however, for ease of manufacturing and bulkdimensional stability.

As an example, thermo-electric texturing of a sodium aluminosilicateglass substrate was carried out at 250° C. This glass has a nominalcomposition, expressed as weight percent of oxides, of 66% SiO₂, 13.6%Al₂O₃, 13.7% Na₂O, 1.7% K₂O, 4.0% MgO, 0.5% CaO, 0.4% SnO₂ and 0.02%Fe₂O₃, and has a strain point, which can be regarded as a lower boundfor the glass transition range, equal to 563° C. The T_(g) of this glassis approximately 613° C.

The process is applicable to a wide variety of glass substrates.Suitable glass substrates can have a thickness ranging from about 0.3 to3 mm, for example. Alkali-rich, low-resistivity glasses can generally betextured at lower temperatures ranging from 25° C. to T_(g)150° C.,e.g., in the range of 100° C. up to 300° C. or (T_(g)-150° C.),whichever is lower. Nominally alkali-free (<1 mol. % alkali) glassesgenerally exhibit higher-resistivity, and can be textured using higherrelative processing temperatures from 250° C. to T_(g)-150° C., e.g., inthe range of 350° C. up to 600° C. or (T_(g)-150° C.), whichever islower. During texturing, the glass substrate can be maintained at asuitable temperature by heating or by cooling. The disclosed texturingmethod can be implemented at the bottom of a draw, for instance, orduring a glass annealing step. Moreover, the glass substrate can beheated or cooled locally (i.e., proximate to the glass surface) orglobally (i.e., such that temperature is controlled over substantiallyall of the glass substrate).

The resulting textured glass substrate includes a locally-modifiedcomposition that is commensurate with the imparted texture. It has beenshown experimentally that the migration of ions within the glass underDC bias changes the near-surface composition of the substrate such thatthe compositional changes are laterally heterogeneous and commensuratewith the induced texture. Specifically, the ion migration results in adepletion of ions only in regions of electrical contact with the “high”points on the template (which correspond to the “low” points on theresulting textured glass surface). This effect is illustratedschematically in FIG. 1.

In FIG. 1, a template electrode 100 has a plurality of raised features110. Distal ends 112 of respective raised features are placed inphysical contact with a surface 152 of a glass substrate 150. Under theeffect of applied temperature and voltage, ion migration is induced inthe glass substrate, which creates in a plurality of ion-depletionregions 160 and an attendant local reduction of glass volume proximatethe raised features of the template electrode.

Throughout the process, contact (i.e., physical contact or electricalcontact) can be maintained between the template electrode and the glasssubstrate, for example, due to the effects of electrostatic pressure atthe interface. Contact can be maintained by moving the electrode as theglass locally recedes, as indicated by the vertical arrows, or by movingthe glass substrate with respect to the electrode, or both

In the resultant textured glass, the composition in the near surfaceregion is depleted of migrated species in those recessed regions thatwere engaged by the electrode. Because ion migration does not occur inregions out of contact with the template electrode, the glasscomposition in the raised regions 170 of the textured glass issubstantially equal to the bulk composition of the substrate. As can beseen with reference to FIG. 1, the “high” points 170 in the texturedglass correspond to the original glass surface (indicated by the dashedline), while the “low” ion-depleted regions 160 in the textured glassare recessed with respect to the original glass surface.

Because the resulting textured glass comprises a compositionalpatterning as well as a spatial texturing, additional optionalprocessing can be readily used to fine-tune the surface texture. In oneembodiment, differential etching can be used to enhance thetopographical aspect ratio. Differential etching can be used because theion depleted zones at the base of the defined features has been observedin some glasses to etch faster than un-affected areas. Acid-etching, forexample, can be used without an etch mask following the thermo-electrictexturing to enhance or fine-tune the surface topographical features.This may be advantageous for applications benefiting from greateraspect-ratio features, such as pillar-like structures.

Glass etching chemistries may include aqueous solutions of hydrofluoricacid (e.g., 1-5 vol. %), or aqueous mixtures of HF or other fluoridecompounds with another mineral acid such as hydrochloric, nitric, orsulfuric acid. High-pH alkaline solutions (e.g. alkali- oralkaline-earth hydroxides) or dry-etch methods may alternatively be usedto achieve the desired differential etch.

In a further embodiment, the texturing process can be used to form arefractive index grating. Because the ion-depleted glass surface willgenerally have a lower refractive index compared to the native glasscomposition, a useful lateral contrast in refractive index may beobserved in addition to and commensurate with the topographical featuresthat are created. Such structure may have applications in optics.

A photograph of a platinum foil used as a template electrode is shown inFIGS. 2A and 2B. The brush-line texture of the foil is more clearly seenwith reference to FIG. 2B, which is a higher magnification image (50×).

With reference to the template electrode images of FIGS. 2A and 2B,corresponding differential interference contrast photographs of atexture-induced sodium aluminosilicate glass substrate and a nominallyalkali-free barium boroaluminosilicate glass are shown in FIGS. 3 and 4,respectively. Optical profilometer height images of the sodiumaluminosilicate glass substrate of FIG. 3 before and after texturing areshown in FIGS. 5A and 5B, respectively.

Topographical height images, height cross-sections, and dimensionsstatistics from (A) a photolithography-textured line template electrode,and (B) a sodium aluminosilicate glass surface having featuresreplicated from the template electrode using the disclosedthermo-electric treatment are shown in FIGS. 6A and 6B. That is, FIG. 6Ashows the texture in the template electrode and FIG. 6B shows thecorresponding texture in the glass substrate. In the FIG. 6 example, theglass was heated to a temperature of 250° C., and the maximum appliedvoltage was 400V.

Shown in FIG. 7 are topographical features replicated on a sodiumaluminosilicate glass surface from a photolithography-textured templateelectrode. FIGS. 7A and 7B show height images from a variety of 1.5 μmto 30 μm-wide line features on the glass surface. FIG. 7C is an examplefeature with a sub-micron lateral dimension. FIG. 7D shows summaryhistograms of z-height distributions from topographical images,indicating a 25-50 nm range of feature depths.

Cross-sectional SEM micrographs of a textured glass substrate are shownin FIG. 8. The 70°-tilt images shown in FIGS. 8A and 8B highlight thetextured topography, while the backscattered image in FIG. 8C revealssubtle evidence of contrast between the unaffected glass region 804 andthe adjacent reduced-height (ion-depleted) regions 802 a and 802 b. Themicrograph in FIG. 8D was obtained after etching the same sample in 1%HF for 1 minute, and both highlights the extent and character of thecompositionally-modified zone, and also demonstrates that the etch ratewithin the network-modifier-depleted, reduced-height regions issubstantially faster than that of the initial glass composition in thisembodiment.

Energy-dispersive x-ray spectroscopy (EDS) plots (A-E) are shown in FIG.9 together with a cross-sectional SEM micrograph depicting thecorresponding sampled regions A-E on a textured sodium aluminosilicateglass substrate. The SEM micrograph shows an unmodified glass regionadjacent point E, and an ion-depleted region adjacent point A. The bulkglass composition at point D is shown in spectrum D. The bulkcomposition D is substantially unchanged at region E and also at regionC, which is about 0.5 micron below the original glass surface. At pointsA and B, however, which lie within the altered zone, a demonstrabledepletion of sodium, magnesium and potassium is observed.

In embodiments, the disclosed process involves providing a templateelectrode, contacting the template electrode with a surface of a glasssubstrate, heating the substrate to a temperature that is less than itsglass transition temperature, and applying a voltage to the electrode toinduce localized ion migration in the glass and form texture in theglass surface. The template electrode is positively biased with respectto the glass. The glass surface in contact with the template electrodemay be referred to as the “anode-side” or “anodic” surface of the glass.The opposite side of the glass may be referred to as the “cathode-side”or “cathodic” surface of the glass.

In order to provide field uniformity over the texturing area, thetemplate electrode material can be more electrically conductive than theglass at the processing temperature. By way of example, the templateelectrode can be formed from or coated with a noble metal or anoxidation-resistant metal Au, Pt, Pd, TiN, TiAlN, etc. Acounter-electrode can be provided on the non-textured side of the glasssubstrate, i.e., the backside, in order to provide for field uniformityover the texturing area.

The electrodes can comprise a bulk material, or a thin film. Forinstance, the electrodes can be separate components that are broughtinto contact with the glass substrate for the texturing step, and thenseparated from the glass. Alternatively, the electrodes, andparticularly the backside cathode, can be a conductive thin film that isformed directly on a surface of the glass. The template electrode can betextured using a variety of methods, including lithography, mechanicalmachining, etc.

During the acts of heating and applying a voltage, the templateelectrode and the glass substrate can be maintained in physical contact.In example embodiments, a flat glass substrate can be textured using aflat template electrode. A shaped or curved glass substrate on the otherhand can be textured using a template electrode having a correspondingshape or curvature. Thus, the template electrode and the glass substratecan be shape-matched to provide electrode-to-glass contact during thetexturing steps at least over the desired texturing area. Even ifinitial contact between the template electrode and the glass surface isnot intimate, the electrostatic pressure created at the interface whenthe voltage is applied can pull the two surfaces into intimate contact.

The general term “glass” is used herein to refer to the substratematerial, but the substrate material is meant to include any of a broadclass of ionically-conductive inorganic materials comprising glasses,glass ceramics, and ceramics that can be formed from a viscous state.

In accordance with one embodiment, a glass substrate may be formed usinga down-draw technique. A glass substrate may comprise a glass ribbon,for example, that may be rolled prior to or following texturing andstored for later use. A typical glass ribbon includes a long dimension L(length L) generally parallel to its drawn edges, and a width Wtransverse to the length.

The glass ribbon may be sized such that texture can be formed across thelength and/or width of the ribbon. In embodiments, texture may be formedon a glass ribbon in a manner analogous to the manner in which imagesare sequentially formed on a strip of photographic film, such that atextured ribbon need only be separated along one dimension to form anindividual device or component, e.g., a display device.

Either before or after to the formation of texture on a glass ribbon,the ribbon can be cut into individual segments. Thus, in one approach,the disclosed texturing process is suitable for batch processing, whilein a second approach the texturing is suitable for continuous orroll-to-roll processing such as in the case of flexible glasssubstrates.

The term “flexible” is generally used to describe the glass substrate,although the substrate need not be flexed during texturing. A flexiblesubstrate is thin enough and has a high enough strength to produce abend radii less than about 30 cm, less than about 10 cm, less than about5 cm, less than about 2 cm, or less than about 1 cm. A continuous orsemi-continuous manufacturing process can be used to fabricate atextured glass substrate, potentially involving a bending of thesubstrate during the process. In other words, a final application forthe textured glass may not require flexing of the substrate, but a costeffective manufacturing process may. A further example involves bendingof a textured glass substrate during use. Devices of componentscomprising textured glass substrates may be manufactured for flexible orconformable applications in either a continuous or flat batch process.

The invention will be further clarified by the following examples.

EXAMPLES 1 AND 2 Brush-Line Texture with Alkali-Rich and NominallyAlkali-Free Glass Substrates

Template electrodes were formed using high-purity platinum (Pt) foil(ESPI; 3N5 purity) having brush-line surface texture. The semi-randomtexture is shown in FIG. 2A and is an inherent result of the processused to draw the foil to its final thickness.

Companion experiments were performed using different glass compositionsunder different conditions.

In one example, flat sodium aluminosilicate glass substrates were usedin conjunction with a Pt foil anode and a counter electrode made usinggraphite foil sheet. After positioning the glass between the electrodes,the assembly was placed into a vacuum chamber at ˜1×10⁻⁴ Torr and heatedto 300° C. After equilibrating at 300° C. for 15 min, 100V was appliedto the anode. An initial increase in current was observed, followed by aslow decay as the depletion layer formed. The current was allowed todecay to 10% of its peak value (limited to 5 mA max), after which thevoltage was stepped up to 200V. With a current decay allowance of 10% ofits peak value at each step, the voltage was increased next to 300V andthen to 400V. Following the voltage ramp, the sample was cooled to roomtemperature, the voltage removed, the chamber vented, and the templateelectrode-glass assembly manually separated.

In a further example, barium boroaluminosilicate flat glass sampleshaving a bulk sodium content of about 500 ppm were used in conjunctionwith the Pt foil anode and a sputter-deposited Pt thin film backsidecathode. As with the previous example, the assembly was placed into avacuum chamber at ˜1×10⁻⁶ Torr. The sample was heated to 600° C. Afterequilibrating at temperature for 15 min, 2,500V was applied to the anodefor 30 minutes. The sample was then cooled to room temperature, thevoltage removed, the chamber vented, and the assembly manuallyseparated.

Photographs of the resulting textured glass substrates are shown inFIGS. 3 and 4, respectively which demonstrating the brush-line texturingon the anode-side glass surface matching that of the template electrodefoil. FIG. 5B shows topographical data from the sodium aluminosilicateglass surface confirming that the optical contrast in the microscopeimage (FIG. 3) is attributable to induced nanoscale topography.

Manual probing corroborated the direct-written texture as a hard,integral parts of the glass surfaces, while XPS and SIMS analysesconfirmed a glassy, locally modifier-depleted composition in bothexamples. Examples 1 and 2 demonstrate the direct-writing ofsemi-arbitrary texture in both alkali-rich and nominally-alkali-freeglass compositions.

EXAMPLE 3 Lithographically-Textured Lines on Sodium AluminosilicateGlass

A template electrode having a well-defined series of features withvarious geometries was prepared using lithographic methods. To form thetemplate electrode, a 300 nm thin film of plasma-enhanced, chemicallyvapor-deposited silica (PECVD SiO₂) was deposited onto a pre-cleanedsilicon substrate. Inter-digitated line texture were incorporated intothe silica layer using traditional lithography. Contact layers of eithertitanium nitride (TiN) or platinum (Pt) were then deposited on thetextured surface to create a conductive template electrode structure.

Flat sodium aluminosilicate glass substrates were textured using thelithographically-prepared template electrodes. A graphite foil was usedas the cathode.

After arranging the glass between the electrodes, the assembly wasplaced into a vacuum chamber at ˜1×10⁻⁴ Torr and heated to 300° C. Afterequilibrating at 300° C. for 15 min, 100V was applied to the anode. Aninitial increase in current was observed, followed by a slow decay asthe depletion layer formed. The current was allowed to decay to 10% ofits peak value (limited to 5 mA max), after which the voltage wasstepped up to 200V. With a current decay allowance of 10% of its peakvalue at each step, the voltage was increased from 200V to 300V and thento 400V. The sample was then cooled to room temperature, the voltageremoved, the chamber vented, and the assembly manually separated.

An example of the line textured replicated from the template electrode(FIG. 6A) onto the glass surface (FIG. 6B) is shown in FIG. 6. Thetextured glass substrate has lateral fidelity to the template electrode.FIG. 7 summarizes topographical data from the glass surface where avariety of feature widths and spacings were used, including asub-micron, 800 nm line as shown in FIG. 7C.

The data in FIG. 7D quantify the feature heights over a range of about30 to 50 nm, suggestive of an intrinsic limitation of heightconformality through some nanoscale range due to the stabilization of adepletion layer in the regions of contact with the template electrode.Manual probing confirmed that the direct-written texture is a hard,integral part of the glass surfaces. The results of cross-sectional SEManalysis of the textured surfaces are summarized in FIGS. 8A and 8B.

Disclosed herein is a process for creating a textured glass surface. Theprocess uses a templated electrode together with the application of heatand an applied voltage to induce localized ion migration thatincorporates into the glass the texture or pattern from the electrode.The process can be carried out at relatively low temperatures, ismaskless, and eliminates the need for chemical etchants or hazardouschemicals to selectively remove material in order to create topography.

In contrast to the application of a film or a coating, the texturedglass surface that is created by the disclosed process is innately partof the original glass article, and therefore the texturing is monolithicto the underlying glass substrate. This results in a robust glasssubstrate that retains the hardness and the mechanical properties of theoriginal glass surface.

Compared to embossing or other alternate methods, the relatively lowprocessing temperatures and relatively short processing times associatedwith the disclosed approach mean that a textured glass substrate can beprepared with minimal geometric distortion or change in the originalsubstrate dimensions, and without adversely affecting other materiallayers or device architectures indigenous to the substrate. The processcan be used to create texture with nanometer-scale dimensions, which maybe particularly suitable to avoiding light-scattering in a variety ofdisplay or cover glass applications.

Additional applications for the textured glass substrates includeanti-reflection, anti-fogging (super hydrophilic),anti-smudge/anti-fingerprint, anti-fouling (when coated with hydrophobicchemistries such as fluorosilane) as well as combinations of theseattributes.

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to an “alkali metal oxide” includes examples havingtwo or more such “alkali metal oxides” unless the context clearlyindicates otherwise.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, examples include from the one particular value and/or to theother particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another aspect. It will be furtherunderstood that the endpoints of each of the ranges are significant bothin relation to the other endpoint, and independently of the otherendpoint.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is no way intended thatany particular order be inferred.

It is also noted that recitations herein refer to a component of thepresent invention being “configured” or “adapted to” function in aparticular way. In this respect, such a component is “configured” or“adapted to” embody a particular property, or function in a particularmanner, where such recitations are structural recitations as opposed torecitations of intended use. More specifically, the references herein tothe manner in which a component is “configured” or “adapted to” denotesan existing physical condition of the component and, as such, is to betaken as a definite recitation of the structural characteristics of thecomponent.

While various features, elements or steps of particular embodiments maybe disclosed using the transitional phrase “comprising,” it is to beunderstood that alternative embodiments, including those that may bedescribed using the transitional phrases “consisting” or “consistingessentially of,” are implied. Thus, for example, implied alternativeembodiments to a glass substrate that comprises a glass material includeembodiments where a glass substrate consists of a glass material andembodiments where a glass substrate consists essentially of a glassmaterial.

Various modifications and variations can be made to the presentdisclosure without departing from the scope of the invention. Sincemodifications, combinations, sub-combinations, and variations of thedisclosed embodiments incorporating the substance of the invention mayoccur to persons skilled in the art, the invention should be construedto include everything within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A method for forming texture in a surface of aglass substrate, comprising: contacting a glass surface of a glasssubstrate having a glass transition temperature and a templateelectrode; heating the electrode-contacted glass surface to below theglass transition temperature; and applying a DC bias to the electrodeeffective to transport ions within the glass surface and form a texturedglass surface.
 2. The method according to claim 1, wherein the textureof the textured glass surface is selected from the group consisting ofbumps, divots, hillocks, pillars, lines, gratings, arrays and channels.3. The method according to claim 1, wherein the texture of the texturedglass surface is at least one negative topographical image of a positivetopographical image on the electrode.
 4. The method according to claim1, wherein the electrode is maintained in physical contact with theglass surface during the heating and applying the DC bias.
 5. The methodaccording to claim 1, wherein contacting the glass surface and thetemplate electrode comprises relative movement of the glass substrateand the electrode while maintaining physical contact during thesimultaneous heating and applying the DC bias.
 6. The method accordingto claim 1, wherein heating the glass surface includes heating orcooling to at least 150° C. less than the glass transition temperature.7. The method according to claim 1, wherein heating the glass surfaceincludes heating from 100 to 300° C.
 8. The method according to claim 1,wherein heating the glass surface includes heating from 300 to 600° C.9. The method according to claim 1, wherein applying the DC bias to theelectrode positively biases the electrode relative to the glasssubstrate.
 10. The method according to claim 1, wherein the DC bias isat a constant magnitude.
 11. The method according to claim 1, whereinapplying the DC bias is accomplished in a plurality of discrete steps.12. The method according to claim 1, wherein the bulk composition of theglass substrate includes less than 1 mol % alkali metal oxide oralkaline earth metal oxide.
 13. The method according to claim 1, whereinthe bulk composition of the glass substrate includes less than 1 mol %alkali metal oxide.
 14. The method according to claim 1, furthercomprising acid etching the textured glass substrate.
 15. A method forforming texture in a surface of a glass substrate, comprising:contacting a glass surface of a glass substrate and a template electrodeat from 20° C. to less than the glass transition temperature of thesubstrate; and applying a DC bias to the electrode effective totransport ions within the glass substrate and form a textured glasssurface.
 16. The method according to claim 15, wherein the contactingand applying are accomplished simultaneously, sequentially, or acombination thereof.
 17. An article comprising: a glass having a bulkcomposition; and a textured region on a surface of the glass, whereinthe textured region comprises a plurality of first features havingsubstantially the same composition as the bulk composition, and aplurality of second features that are lowered with respect to the firstfeature and which have a depleted composition in at least one of analkali, an alkaline earth, a transition metal, or a combination thereofwith respect to the bulk composition.
 18. The article according to claim17, wherein the depleted composition has an alkali, alkaline earth, ortransition metal composition that is less than 50% of the bulkcomposition (in mol %).
 19. The article according to claim 17, whereinthe depleted composition has an alkali, alkaline earth, or transitionmetal composition that is less than 10% of the bulk composition (in mol%).
 20. The article according to claim 17 wherein the bulk compositionof the glass has less than 1 mol % alkali metal oxide.
 21. The articleaccording to claim 17, wherein the bulk composition of the glass hasless than 1 mol % alkali metal oxide, and less than 1 mol % alkalineearth metal oxide.